1. Field of the Invention
This invention relates to methods (processes) for making relatively thick foraminous members the foramina of which form a preselected pattern.
2. Background Art
Stencil screens for printing or the application of inks, pigments, and the like have been used by industry for a number of years. For example, stencil screens used in the ceramics industry generally comprise a stainless steel screen of relatively fine mesh size the interstices of which have all been closed except for those which define the design which is intended to be printed. The design is printed by placing the stencil screen in contact with the surface and forcing ink, pigment, or the like through the open meshes. Such stencil screens are conveniently prepared with the aid of a photosensitive material such as a photosensitive resin. In general, the screen is coated with a relatively thin layer of photosensitive material which is then exposed to light of the requisite wavelength through a mask or photographic film containing a positive image of the design to be printed. That is to say, the design one wishes to print appears in the mask as regions which are opaque to light. During exposure, the resin which is unprotected by the design of the mask partially cures or hardens while that portion of the resin protected by the opaque design remains uncured and fluid. The uncured, fluid portion of the resin can then be removed and washed from the screen leaving a system of open interstices defining the pattern to be printed. Numerous patents and other references describe various and sundry techniques for making stencil screens. Examples include U.S. Pat. No. 2,860,576 issued to Short on Nov. 18, 1958 and U.S. Pat. No. 4,291,116 issued to Tibbetts on Sept. 22, 1981.
Certain industrial operations other than printing also require the use of foraminous members the open regions of which define some preselected pattern. Unlike printing operations, these other industrial operations require a foraminous member having a significantly greater thickness than that provided by common stencil screens. Further, these other industrial operations sometimes require foraminous members having sizes significantly greater than those commonly found in stencil screens. In certain operations, the foraminous member is required to be in the form of an endless belt which can be, for example, 6 meters wide by 75 meters long.